1. Field of the Invention
This invention relates to a new use of cationic layered materials, compositions comprising these materials, and a process for the preparation of cationic layered materials.
2. Prior Art
A Cationic Layered Material (CLM) is a crystalline NH4-Me(II)-TM-O phase with a characteristic X-ray diffraction pattern. In this structure, Me(II) represents a divalent metal and TM stands for a transition metal. The structure of a CLM consists of negatively charged layers of divalent metal octrahedra and transition metal tetrahedra with charge-compensating cations sandwiched between these layers.
The CLM structure is related to that of hydrotalcite and hydrotalcite-like materials. These materials, also referred to by the skilled person as layered double hydroxides (LDH) or anionic clays, are built up of Me(II)-Al hydroxide sheets with exchangeable anions in the interlayers. Analogous to the term “anionic clay” being a synonym for hydrotalcites and hydrotalcite-like materials, “cationic clay” can be used as a synonym for CLM.
CLMs are known from the prior art. M. P. Astier et al. (Ann. Chim. Fr. Vol. 12, 1987, pp. 337–343) prepare CLMs by first dissolving ammonium hepta molybdate and nickel nitrate in an aqueous ammonia solution and subsequently altering the pH by evaporating ammonia, resulting in precipitation. After aging, washing, and drying, pure crystalline CLMs are formed with a characteristic X-ray diffraction pattern.
A similar precipitation procedure is disclosed in U.S. Pat. No. 6,156,695 for the preparation of CLMs containing Ni, W, and Mo.
D. Levin, S. Soled, and J. Ying (Chem. Mater. Vol. 8, 1996, pp.836–843; ACS Symp. Ser. Vol. 622, 1996, pp. 237–249; Stud. Surf, Sci. Catal. Vol. 118, 1998, pp. 359–367) also disclose the preparation of CLMs. Their process involves the steps of (a) precipitating a divalent metal salt and aluminium nitrate, (b) aging the precipitate to form an anionic clay, (c) calcining the anionic clay to form a mixed oxide, and (d) contacting and reacting the mixed oxide with ammonium heptamolybdate—thereby removing aluminium ions and incorporating molybdate ions—resulting in a CLM with a trace amount, e.g. 0.63 wt %, of aluminium.
It has been found that CLMs can suitably be used in or as a catalyst or catalyst additive in a hydrocarbon conversion, purification, or synthesis process, particularly in the oil refining industry and Fischer-Tropsch processes. Examples of processes where CLMs can suitably be used are catalytic cracking, hydrogenation, dehydrogenation, hydrocracking, hydroprocessing (hydrodenitrogenation, hydrodesulfurization, hydrodemetallisation), polymerisation, steam reforming, base-catalysed reactions, Fischer-Tropsch, and the reduction of SOx and NOx emissions. They are especially suitable for use in FCC processes, particularly as active material in FCC catalysts or catalyst additives for (i) the reduction of the nitrogen and/or sulfur content of fuels like gasoline and/or diesel and/or (ii) the reduction of SOx and/or NOx emissions.